Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for use in vehicle suspension. Particular embodiments of the invention relate to methods and apparatus useful for variable spring rate and/or variable damping rate vehicle suspension.
Description of the Related Art
Vehicle suspension systems typically include a spring component or components and a damping component or components. Frequently those discrete components are separately mounted on a vehicle. Traditionally, mechanical springs, such as metal leaf or helical springs, have been used in conjunction with some type of viscous fluid based damping mechanism mounted functionally in parallel. More recently, compressed gas acting over a piston area has replaced mechanical springs as the spring component in some contemporary suspension systems. While compressed gas springs are usually lighter and more compact than their mechanical counterparts, the compression and expansion curve and corresponding spring rate, are not linear and become particularly exponential beyond a mid range of gas compression.
As such, the force (corresponding to pressure acting on a given piston area) versus the linear travel or displacement of the air spring is not linear. While a gas spring force curve approximates linearity during an initial portion of travel, the last portion of travel is exponential. The shock absorber is therefore increasingly more rigid in the last portion of its stroke.
Accordingly, there is a need for a shock absorber that uses a multiple volume gas spring under a variety of loads and/or under a variety of travel settings.